Yuri Blanarovich wrote:
"Roy Lewallen" wrote in message

The currents flowing different directions don't cancel. If they flow in
equal amounts, in phase, in opposite directions, then the fields they
create nearly cancel. And that's the case along the roof of a car if the
car and roof are symmetrical and the antenna is at the center. But it's
not the case where it flows vertically along the sides of the car. There,
the currents are in the same direction.


How do YOU make it flow vertically along the sides of the car and not
distributed along the whole conductive surface of the car's body? How do you
make the current flowing, say, towards the front of the car (or one side)
not to (partially) cancel by current flowing in opposite deirection, towards
the back (or other side)?

I don't make it flow anywhere. The field from the current flowing toward
the front, along the roof, cancels the field from the current flowing
toward the rear along the roof. Once the current reaches the edge of the
roof, all components flow vertically. If the car is symmetrical and the
antenna mounted in the center, all components are in phase. There is no
field or potential gradient to induce current flow horizontally along
the sides, front, and back of the car.

The currents flow from the feed point, base of the vertical in all
directions where supported by conductive sheet metal, or wire or radial.
They might not be exactly symmetrical, but they have opposite direction
portion of the current and corresponding cancellation.

Along the roof, yes, as I explained in my original posting. But they
don't flow in opposite directions along the sides, front, and back of
the car.

The radiation pattern is formed by the sum of all the fields which are
created by currents flowing on conductors. The antenna is one such
conductor. The body of the car is another.


How simple! :-)

Yes, it is indeed.

Please model vertical resonant dipole, then monopole with one radial, then
with two radials, then with 8 radials, then with 64, then with solid sheet,
then with car body. Then move the antenna around, away from the center and
see what happens to the pattern. See how this "conductor" is "another".
Then the case of say 2m quarter wave vertical mounted in the middle of the
roof, sure doesn't look like car is the other wire.

If you're saying that a car doesn't look like a 19 inch wire, you're
right. It doesn't look like the Earth, either.

That's true. And the coupling of the car body to ground alters the amount
of current flowing along the body of the car. This current equals the
current flowing into the antenna.


That is true, but portions of the current flowing in different directions
from the feedpoint are in opposite direction and based on their magnitude
partially cancel. The result is the interaction with monopole, radiator and
forming the radiation pattern, which in practical HF mobile installation is
distorted, lopsided. If it was the"other wire" then it would be symmetrical
like in true vertical symmetrical di-pole.

Sigh. You're right, it's not like a symmetrical dipole. It's like a Yuri
Special asymmetrical dipole.

Suit yourself. I called the system an "asymmetrical dipole". But like
"ground", putting a name on it doesn't change its properties.


I am not suiting myself but describing difference between vertical monopole
working against conductive surface (sheet, car body, radials) with
corresponding current flow and dipole, di-pole that customarily refers to
symmetrical antenna with two (similar) legs.

Ok.

Certainly a whip mounted on a vehicle can be expected to have a different
pattern than a symmetrical dipole, and nothing I've written has attempted
to make a claim that it does. But it sounds like you've grabbed onto the
"asymmetrical dipole" label as a basis for argument. So please go back
over my postings but substitute "Yuri special" for "asymmetrical dipole"
and see if then you find anything I've written which isn't correct.


Sounds more like "Roy special" - everything is assymetrical or symmetrical
dipole. How "dipoly" is the 2 m whip in the middle of the car roof? How can
you tune to resonance 80 m car whip by adjusting the "other wire" - car
body? Implying the other half of "Roy dipole" is a "wire"?

My comments were made when envisioning an HF antenna. I believe that if
you move the same HF antenna from one car to another, or change the
mounting position, the resonance will change. Haven't you found this to
be true? At VHF the asymmetry is of course much greater, and the short,
thin part (the whip) of a structure like the VHF whip-car combination
has much more effect on the impedance than the long, fat part (the car).

That's the way I understand it, without involving photons, Gaussss and
other farticles :-)
If you say so.


Other smarter people in their books and modeling in your EZNEC say so.

Roy Lewallen, W7EL